Plastic escapement lever

ABSTRACT

A plastic lever having plastic pallet pins projecting therefrom for cooperation with an escape wheel, the pallet pins each comprising a relatively small active portion supported by a substantially larger reinforcing portion with both portions being smoothly faired to cooperate with the escape wheel teeth in an anti-locking manner upon reverse power application to the escape wheel.

United States Patent [191 Lawson PLASTIC ESCAPEMENT LEVER [75] Inventor:

[73] Assignee: Bunker Ramo Corporation, Oak

- Brook, Ill.

[22] Filed: June 29, 1972 [21] Appl. No.: 267,334

Robert R. Lawson, Somerset, Wis.

[52] US. Cl 58/116 R [51] Int. Cl. G04b 15/00 [58] Field of Search 58/116-118, 58/120-122; 74/15 [56] t References Cited UNITED STATES PATENTS 3,425,212 2/1969 Verde 58/116 R 2,481,213 9/1949 Gummersall.... 58/116 R 7 2,706,884 4/1955 Fidelman 58/117 [451 Apr. 16, 1974 3,446,007 5/1969 Cohen 58/116 R FOREIGN PATENTS OR APPLICATIONS 240,640 5/1946 Switzerland 58/116 R Primary Examiner-George H. Miller, Jr. Attorney, Agent, or FirmD. R. Bair; F. M. Arbuckle [5 7] ABSTRACT A plastic lever having plastic pallet pins projecting therefrom for cooperation with an escape wheel, the pallet pins each comprising a relatively small active portion supported by a substantially larger reinforcing portion with both portions being smoothly faired to cooperate with the escape wheel teeth in an antilocking manner upon reverse power application to the escape wheel.

8 Claims, 5 Drawing Figures 1 :PLASTIC ESCAPEMENT LEVER -metal pieces mounted ina'plastic lever. In such con-' structions, the impulse pins often lean out of alignment, causing, at best, poor escapement action, and often requiring rejection at quality control inspection and loss of the affected parts; Further, metal pallet pins have typically caused excessive rebound resulting from the inherent springiness of the metal pins.

An important object of the present invention is to overcome such disadvantages of prior structures and to attain important improvements and advantages in clockwork escapement systems.

Another object of the invention is to provide a new and'improved plastic pallet pin andlever construction.

A further object of the invention'is to provide anew and improved one-piece plastic pallet pin and lever unit.

Still'another object of the invention is to provide a new and improved operative relationship between the escapement lever and escape wheel in an escapement system preventing reverse motion lock-up and smooth forward energy release.

Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawing, although variations and modificationsmay be effected without departing from the spirit and scope of the novel concepts embodied in the disclosure, and in which:

FIG. 1 is a fragmentary 'side-elevational view of a timepiece movement showing a balance wheel and escapement system embodying features of the invention;

FIG. 2 is an enlarged fragmentary sectional plan detail view taken substantially along the line IIII of FIG. 1; j

FIG. 3 is a substantially enlarged plan view of the novel pallet pin in reverse power engagement with the escape wheel;

FIG. 4 is an enlarged. partial plan view of the lever and escape wheel with the receiving pallet pin engaged with the escape wheel; and

FIG. 5 is an enlarged partial plan view of the lever and escape wheel with the let-off pin in engagement with the escape wheel.

Although features of the invention may be employed in any clockwork, whether of the smller watch sizes or larger clock sizes, special advantage has been found for the invention as embodied in automobile clockworks. Automobile clocks of necessity require rugged structure capable of withstanding extremes of temperature as well as often excessive shocks encounterd in and during operation of the associated automobile. A typical example of a clockwork embodying features of the invention, as represented in FIG. 1, includes spaced frame plates 10 and 11 providing suitable bearings for the journals of an escape wheel staff 12, an escape lever staff l3and a balance wheel staff 14. Carried by the es cape wheel staff 12 is a pinion l5 meshing with a gear 17 operatively coupling the associated clock movement with the balance wheel and escape assembly. The pinion 15 is mounted adjacent to one end of the staff 12 and carried in balanced relation adjacent to the opposite endof the staff 12 is an escape wheel 18 controlled by an escape lever l9carried by the staff 13.

Impulse pin and guard roller means are provided on and in association with the balance wheel staff 14 and a balance wheel 20 carried corotatably thereby. Preferably, a combination, one-piece molded plastic guard roller and impulse pin unit 21 is provided. The unit 21 may be made from any suitable moldable plastic, such as an acetal copolymer resin, readily available commercially under the trademarks Celcon and Delrin. The details of construction and operation of the guard rollers are fully set forth in copending application for US. Pat. Ser. No. 259,863 filed June 5, 1972 and entitled TIMEPIECE ESCAPEMENT.

According to the present invention, the escape lever 19 is also desirably a molded plastic part which may be made from similar material as the guard roller and impulse pin unit 21. Assembly of the lever 119 with the lever staff 13 is adapted to be effected by a relative axial press fit wherein the staff is received in and through a hub 29 on the lever. As shown, the lever 19 is of elongated form and is pivotally mounted by means of the staff l3adjacent to and in partially overlying relation to peripheral teeth 30 of the escape wheel 18. Respective escape lever pins or pallet pins 31,32 integral with adapted lever and suitably spaced and oriented in position on the lever are dapted for efficient alternate timing coaction with the successive teeth 30 upon oscillation of the lever under the controlof the balance wheel assembly.

At its end farthest from the pivot provided by the staff 13', the lever 19 has a fork 35 within which the impulse pin 28 is received. Also on the fork end of the lever 19 and aligned in spaced relationto the fork notch is a guard finger 33 which extends into the roller notch 23. As will be apparent in the particular arrangement shown, the lever 19 is relatively closely spaced with respect to, and overlies the escape wheel 18 for an especially compact assembly in which the pallet pins 31,32 as well as the finger 33 may be molded integrally in one piece with the lever 19, with the pins 31,32 accurately formed and positioned for optimum effectiveness without any possibility of improper orientation or leaning as is frequently experienced where such pins are separately formed and are mechanically attached to the lever.

To provide a simple and inexpensive escapement, it is important that the components be manufacturable with a minimum assembly and adjustment time. As above noted, it has been suggested that a simple escapement might employ a plastic lever in combination with a pair of upstanding metal pin members permanently inserted therein. Use of cylindrical metal pins was suggested as a relatively inexpensive mechanism. However, construction of such an escapement proved that although the cylindrical pin member itself is a rela tively inexpensive structure, the satisfactory assembly of a pin into the lever in a consistently accurate position is extremely difficult. Further, utilization of relatively small diameter metal pins, in a diameter optimum for the locking and unlocking action of the escapement, proved, in combination with a plastic lever, to be excessively resilient and caused undesired rebound during operation. Enlargement of the diameter of the metal pins adversely affects the general operation of the system, and, although minimizing rebound action, retained the built-in manufacturing problems inherent in precisely assembling the pins into the plastic lever.

In accordance with this invention, the metallic pins are molded integrally with the plastic lever and, at the same time, are provided with active surfaces of substantially the same dimension as the proposed small diameter cylindrical metal pin. Plastic materials, such as described above in this specification, are of sufficient strength if reinforced by substantial volume of plastic material and we have found that when so constructed and reinforced, the resiliency of the pallet pin is substantially less than that of the small diameter metal pin previously considered, and an improved action is obtained. Utilization of reinforcing volumes of plastic material has, however, posed a problem not present when small diameter metal pins are employed. Upon reverse power application at the escapement wheel, an impact jamming or locking action was found to occur occasionally. Through the utilization of faired surfaces, as shown herein this problem has been eliminated.

As can be seen from a consideration of the drawings, the lever 19 of the present invention is constructed integrally with the pallet pins 31 and 32. Each of the pallet pins 31 and 32 is provided with an active portion and a reinforcing portion. As can best be seen from FIGS. 3, 4 and 5, the active portion of the pallet pin 31 is indicated at 31a while the reinforcing portion is indicated at 31b. With the rotation of the escapement wheel 18 in a counterclockwise direction as viewed in FIGS.-4 and 5, the operating portion 31a of the pallet 31 has two areas of contact, namely, area 31c which may be termed the leading edge of the pallet pin and which contacts the locking face a of a respective escapement tooth 30. The other surface is the banking or rebound surface 31d which cooperates with the tooth surface 30b between respective teeth 30 of the escapement wheel.

The operating portion comprising the curved surfaces 31c and 31d is substantially the same as a small pallet pin. An operating portion of 0.010 inches diameter has proven satisfactory. However, if the surfaces 31c, 31d were to be continued into a cylinder, or pin, rather than being otherwise supported, the pin would have even more unsatisfactory characteristics than if it were metal. The plastic would be essentially more resilient than metal and would, additionally, be more likely to break in use. In accordance with the present invention, a very substantially larger volume of plastic is pro vided in the reinforcing portion 31b. As shown, the reinforcing portion is 0.040 inches, or about four times that of the operating portion. By providing the pallet 31 with a substantial length generally along its axis line 3le, very substantial rigidity is imparted to the pallet in the direction of impact, the stiffness of the pallet minimizing rebound when the pallet surface 31d strikes the root 30b of the escape wheel 18 as the lever 19 pivots in the clockwise direction about the staff 13a as viewed in FIG. 4. This stiffness is also important in absorbing the impulse delivered by the impulse face 30c which occurs as the lever 19 moves in the counterclockwise direction following its unlocking of the locking surface 30a.

Operation of the escapement in its usual running condition is clearly understood from FIGS. 4 and 5. In FIG. 4, the lever 19 has moved to its extreme clockwise direction under the influence of the balance wheel 20 controlled by hair spring 36 and transmitted to the lever 19 by the impulse pin 28. As the pallet 31 assumes the position shown in FIG. 4, the locking face 30a of the escape wheel 18 prevents movement of the escape wheel in the counterclockwise direction until the lever 19 moves counterclockwise about its pivot axis 13a. As the balance wheel 20 oscillates in its return path, the impulse pin 28 reengages the lever 19 in the manner well known in the art causing the lever 19 to move in the counterclockwise direction. As surface portion 310 moves downwardly as viewed in FIG. 4, the surface 31c slides along the locking face 30a until it passes the corner 30f, at which time the impulse face 300 rides across the end of the pallet pin 31 applying energy to the lever 19 and thence to the balance wheel by way of the impulse pin 28. It will be observed that in the escapement illustrated, the locking face 300 is at an angle 6 to the radius line 41 such that as the lever 19 moves in a counterclockwise direction to disengage from the escapement wheel, the escape wheel backs up, or recoils, in the clockwise direction for disengagement.

As the lever 19 continues to move in the counterclockwise direction under the impulse applied by impulse face 30c, the pallet 32 moves toward the center of rotation of the escape wheel 18 to intercept the locking face 30a of the next upcoming escape tooth 30. As the impulse pin 28 disengages from the lever 19 the let off pallet 32 engages the escape wheel as shown in FIG. 5. Between the positions of FIGS. 4 and 5, the escape wheel will have rotated approximately one-half tooth.

In the normal operation of the escapement, the oscillation of the lever 19 regulates, by its intermittent motion, release of the escapement wheel. Since the balance wheel 20 oscillates regularly under the influence of the impulses delivered by the surface 30c of the escapement teeth 30, as applied sequentially to the pallets 31 and 32, accurate time-keeping is assured. By providing a relatively thin nosed operative portion 31a and 32a, on each of the pallets 31 and 32 respectively, swinging movement of the lever 19 is accomplished without interference with the teeth 30 of the escape wheel. Thus, clearance is provided at 42, as shown in FIG. 5, and at 43, as shown in FIG. 4. Provision of this clearance does not prevent stiffness and rigidity of the pallets, however, in view of the reinforcing portions 31b and 32b, respectively. However, utilization of substantially larger volume reinforcing portions creates a possibility of a locking action on reverse power application. For example, where an escapement of the type above described is employed in an automobile clock which is intermittently wound by the application of energy to a spring, a momentary reverse power application to the escapement wheel 18 occurs. If, for example, the escapement were in the condition shown in FIG. 5 and a wind-up power application were applied to the elock, the escape wheel 18 would rotate in the counterclockwise direction as shown in FIG. 3, causing the let-off pallet 32 to intercept the corner d of the tooth 30. It has been found that by fairing the surface 45 of the pallet 32, for example, from the point of root contact 32 around to the point of contact with the es cape tooth point 30d, no sharp corners or notches are provided in which the escape wheel can jam itself. It will be realized that when the escapement is in the condition shown in FIG. 5, for example, a reverse rotation of the escape wheel 18 cannot significantly cause clockwise rotation of the lever 19 since it is locked in its shown position by the roller 21 until such time as the balance wheel swings back on its regular oscillation. Accordingly, a tendency exists, unless the design is as shown, for the escape wheel to dig into the plastic pallet 32, or 31, as the case may be, unless the rear surface 45 is contoured to prevent lock-up. Lockup is most effectively prevented when the impulse surface 300 makes an angle 1) greater than 90 with the tangent drawn to the surface of the reinforcing portion, or post, of the pallet. As can be seen, this rear surface preferably takes the form of a reentrant curve which provides maximum clearance 42,43 adjacent the operating tip portion of the pallet pin coupled with a smoothly flowing, or faired, contour culminating in a surface lying flat, or nearly so, against the point 30d of the successive escapement tooth.

For a given permitted manufacturing tolerance, the

, neck 31g should be a maximum thickness in order to maximize stiffness of the pallet pin. Preferably, therefore, the front clearance distance dimension A, comprising the distance between the neck 31lg and the locking face 300, should substantially equal the rear clear 'ance dimension. The rear clearance comprises the clearance 42 at its minimum, when the let-off pallet 32 just passes over the corner 30f.

it will be observed that the design of escapement shown herein lends itself particularly well to mass production. The shapes are readily molded in plastic and the pallet pins have a dumb bell shape which can easily bank on the root of the escape wheel without significant flexibility, and at the same time, no abrupt corners or notches are available to permit the sharp point of the escape wheel teeth to dig into or jam with the pallet pin in a manner to jam the escapement upon reverse power application, during winding or under impact jars. The escape wheel tooth shown is similarly readily molded in plastic compared to the typical escapement wheel formed for operation with sharp angularly walled jeweled lever escapements of the classic form. The present escapement has the advantages of a pin escapement without the disadvantages heretofore observed in such escapements and is capable of extremely accurate construction with no assembly requirements relative to the leverand pallet pins..Elimination of excessive rebound while at the same time providing for plastic pallets, lever and escapement wheel has permitted a substantial reduction in cost resulting from savings in material and from elimination of extremely critical assembly operations. it will be apparent to those skilled in the art that variations and modifications may be made in the structure illustrated above without departing from the novel concepts of our invention. It is, accordingly, my intent said lever in a direction parallel to the pivot axis of said lever and said escapement wheel for cooperation with escape teeth on said escapement wheel, each of said pins being of generally cylindrical form and of elongated generally paddle-shaped cross-section with the longitudinal axis of the cross-section lying generally radially of the escapement wheel whereby one end of said cross-section engages said wheel and the other end supplies stiffening reinforcement for said one end generally in the direction of impact between said pin and 7 said escapement wheel and escape teeth, said one end being substantially smaller in width than the width between adjacent teeth on said escapement wheel.

2. The escapement set forth in claim 1 wherein said other end is substantially larger than said one end.

3. The structure set forth in claim 1 wherein the said one end comprises a substantially rounded radius having a width approximately .OlO inches.

4. The escapement set forth in claim 3 wherein said I larger end is approximately four times as large as said one end.

5. The structure of claim 1 wherein one end is connected to said otherend in a smooth faired curve offering no abrupt retention surfaces to said escape wheel teeth upon reverse direction of travel.

6. The structure of claim 5 wherein the escape wheel is provided with teeth each having an impulse surface and wherein a tangent to the pallet pin at the point of contact with said impulse surface makes an angle in excess of to minimize locking retention of the escapement wheel upon reverse rotation thereof under conditions of rewind or jarring.

7. A plastic pin type escapement comprising a plastic escapement wheel adaptedfor cooperation with a small diameter pin, and a plastic escape lever carrying a pair of pins integral therewith, each said pin having a contact portion of approximately said small diameter and a reinforcing portion extending generally radially away from said escape wheel, said reinforcing portion being substantially larger than said contact portion and said portions being connected by an uninterrupted smoothly faired curve portion providing reverse rotation contact areas between said escape teeth and said pin generally parallel to each other to minimize escapement lock-up upon reverse rotation therebetween.

8. The structure of claim 7 wherein the maximum clearance between said faired curve portion and an adjacent contacted tooth of the escapement wheel in the forward locked condition substantially equals the minimum clearance between said pallet pin and the next successive tooth when the pallet pin is unlocked. 

1. In combination in an escapement for clocks or the like having an intermittently wound power source normally biased in one direction for driving an escapement wheel, a pivotal escapement lever drivingly connected to an oscillating balance wheel for controlling said escapement wheel under the influence of said balance wheel, a pair of pallet pin members projecting from said lever in a direction parallel to the pivot axis of said lever and said escapement wheel for cooperation with escape teeth on said escapement wheel, each of said pins being of generally cylindrical form and of elongated generally paddle-shaped crosssection with the longitudinal axis of the cross-section lying generally radially of the escapement wheel whereby one end of said cross-section engages said wheel and the other end supplies stiffening reinforcement for said one end generally in the direction of impact between said pin and said escapement wheel and escape teeth, said one end being substantially smaller in width than the width between adjacent teeth on said escapement wheel.
 2. The escapement set forth in claim 1 wherein said other end is substantially larger than said one end.
 3. The structure set forth in claim 1 wherein the said one end comprises a substantially rounded radius having a width approximately .010 inches.
 4. The escapement set forth in claim 3 wherein said larger end is approximately four times as large as said one end.
 5. The structure of claim 1 wherein one end is connected to said other end in a smooth faired curve offering no abrupt retention surfaces to said escape wheel teeth upon reverse direction of travel.
 6. The structurE of claim 5 wherein the escape wheel is provided with teeth each having an impulse surface and wherein a tangent to the pallet pin at the point of contact with said impulse surface makes an angle in excess of 90* to minimize locking retention of the escapement wheel upon reverse rotation thereof under conditions of rewind or jarring.
 7. A plastic pin type escapement comprising a plastic escapement wheel adapted for cooperation with a small diameter pin, and a plastic escape lever carrying a pair of pins integral therewith, each said pin having a contact portion of approximately said small diameter and a reinforcing portion extending generally radially away from said escape wheel, said reinforcing portion being substantially larger than said contact portion and said portions being connected by an uninterrupted smoothly faired curve portion providing reverse rotation contact areas between said escape teeth and said pin generally parallel to each other to minimize escapement lock-up upon reverse rotation therebetween.
 8. The structure of claim 7 wherein the maximum clearance between said faired curve portion and an adjacent contacted tooth of the escapement wheel in the forward locked condition substantially equals the minimum clearance between said pallet pin and the next successive tooth when the pallet pin is unlocked. 